Our invention comprises improvements in an automotive air conditioning compressor. It relates to the invention disclosed in application Ser. No. 101,110, filed by Duane F. Steele, entitled "Swashplate Compressor for Air Conditioning Systems", filed Sept. 25, 1987. That application is assigned to the assignee of our invention.
Prior art swashplate compressor designs may be seen by referring to U.S. Pat. Nos. 4,381,178; 4,413,955; 4,408,962 and 3,380,651. The designs shown in these prior art references include cylinder bodies in which axially arranged cylinders are machined in angularly spaced relationship about the axis of the compressor. Each cylinder receives a compressor piston, each piston comprising a pair of piston heads joined by a bridge to form an integral, double acting piston. The margin of a swashplate is received within a piston cavity located between each piston head adjacent the bridge. .A sliding swashplate shoe engages the swashplate and is held in place within the piston recess thereby providing a sliding drivable connection between the swashplate and each piston. As the swashplate rotates, the rotary motion of the swashplate is translated into reciprocating motion of the pistons.
The swashplate in the prior art constructions is formed of cast iron or powdered metal, the shoe engaging surfaces of which are machined following the forging operation. The swashplate is joined to a central driveshaft received through a central opening the hub of the swashplate. The swashplate and the driveshaft may be joined by a drive pin as shown in the '178 patent and in the '955 patent, or by a key and slot connection as shown in the '651 patent or by a friction force fit as shown in the '962 patent. The drive pin or the keyway driving connection introduces complexity into the compressor assembly and requires expensive machining operations. The machining operations, aside from the cost and the special machine tools that are required during manufacture, establish stress points which are potential causes of structural failure of the compressor during operation when the swashplate is subjected to high forces. In the prior art designs that employ a press fit between the shaft and the hub of the swashplate, such as in the design of the '962 patent, high stresses are developed as the shaft is pressed into the central opening of the swashplate hub. This requires a relatively large swashplate hub.
The machined surface of the swashplate, as seen in each of the prior art references mentioned above, is engaged by shoes. Each shoe has a recess in which is fitted a drive ball. In turn the ball is received in a recess in the adjacent piston. The ball is formed of high carbon steel, and the shoe is formed of a material having suitable bearing characteristics. Provision is made for establishing an oil film between the shoe and the adjacent surface of the swashplate engaged by the shoe.
Because of the machining operation that the swashplates of prior art designs require, it is necessary in those designs to provide a substantial relief near the hub of the swashplate. This reduces the axial dimension of the finished swashplate and reduces the strength of the swashplate. Because of the presence of the relief adjacent the hub of the swashplate, it is necessary to increase the axial effective width of the swashplate to maintain sufficient strength to withstand the substantial axial forces imposed on the swashplate by the pistons during operation. This avoids breakage of the swashplate as the driveshaft is inserted during manufacture into the central opening of the swashplate hub with a press fit as shown in the '962 patent.